"Marco, a member of the swim team, routinely hyperventilates before a meet, as he says, “to sock some more oxygen into my lungs so I can swim longer without having to breathe.”
Well, for one thing, the hemoglobin in blood leaving the lungs is basically fully saturated with oxygen even under normal breathing conditions, so hyperventilating won’t load any extra oxygen into Marco’s blood. However, hyperventilating does get rid of more than the usual amount of carbon dioxide, lowering its concentration in the blood.
One day, during an especially intense training session when his coach and teammates are not present, Marco loses consciousness in the middle of the pool. He’s found 3 hours later at the bottom with his lungs full of water."

Use what you’ve learned about the physiological controls for breathing to explain what happened.

I am confused as to why Marco passed out. From reading the text book pages I came up with this but I am not sure if it is right:

"The reason Marco lost consciousness because respiration is controlled entirely by receptors that respond to CO2 rather than O2. It's controlled by the need to get rid of CO2 rather than to obtain O2. Since Marco got rid of an unusual amount of CO2 by hyperventilating, the chemical receptors that monitor CO2 didn't single the Medulla Oblongata to produce more O2, since it didn't see that there was more CO2 that it need to get rid of. Because of this, Marco became oxygen starved, ran out of energy, passed out and drowned."